Antimicrobial, Optical and Mechanical Properties of Chitosan-Starch Films with Natural Extracts.

Natural extracts possess several kinds of antioxidants (anthocyanins, betalains, thymol, carvacrol, and resveratrol) that have also demonstrated antimicrobial properties. In order to study these properties, extracts from cranberry, blueberry, beetroot, pomegranate, oregano, pitaya, and resveratrol (from grapes) were obtained. Growth inhibition tests of mesophilic aerobes, coliforms, and fungi were conducted in films prepared from the extracts in accordance with Mexican Official Norms (NOM). Optical properties such as transparency and opacity, mechanical properties, and pH were also analyzed in these materials. The films with beetroot, cranberry, and blueberry extracts demonstrated the best antimicrobial activity against various bacteria and fungi in comparison with unmodified chitosan-starch film. This study shows that the addition of antioxidants improved the antimicrobial performance of these films. It was also found that antimicrobial properties are inherent to the films. These polymers combined with the extracts effectively inhibit or reduce microorganism growth from human and environmental contact; therefore, previous sterilization could be unnecessary in comparison with traditional plastics. The presence of extracts decreased transmittance percentages at 280 and 400 nm, as well as the transparency values, while increasing their opacity values, providing better UV-VIS light barrier properties. Despite diminished glass transition temperatures (Tg), the values obtained are still adequate for food packaging applications.

Design, development, and experimental setup of near-field electrospinning with a sharp electrode: Influence of procedural parameters on the 3D nanofiber structure.

A near-field electrospinning configuration has been developed to fabricate 3D structures by layer-by-layer stacking. The system or experimental setup consists of a high voltage source, a syringe pump, and the electrospinning equipment which has been designed and built. It works with Arduino Uno as a controller for adjusting the procedural parameters through OpenBuilds CONTROL software using a firmware preloaded on the Arduino Uno. The proposed experimental configuration consists of a collinear arrangement between the spinner and the sharp electrode, which move in the XY directions, keeping the same disposition; this arrangement is designed with the aim of manipulating the electric field (EF) and reducing instabilities associated with the process. The displacement speed (DS) and the distance of work adjust automatically to modify nanofiber features, which improves the flexibility of the system. In order to be efficient and set the EF profile, this was simulated using COMSOL Multiphysics® software. Nylon 6,6 polymeric fiber films have been electrospun to evaluate the efficiency of the system setup and the influence of parameters. The fiber morphology is studied by scanning electron microscopy and the chemical structure features are studied by infrared spectroscopy. Parameters such as voltage and DS are studied experimentally and analyzed to determine their effects on the control of fiber deposition. Stacking of up to 15 layers was obtained where the structural characteristics notably depend on the operating parameters.

Chitosan-Starch Films with Natural Extracts: Physical, Chemical, Morphological and Thermal Properties.

The aim of this study is to analyze the properties of a series of polysaccharide composite films, such as apparent density, color, the presence of functional groups, morphology, and thermal stability, as well as the correlation between them and their antimicrobial and optical properties. Natural antioxidants such as anthocyanins (from cranberry; blueberry and pomegranate); betalains (from beetroot and pitaya); resveratrol (from grape); and thymol and carvacrol (from oregano) were added to the films. Few changes in the position and intensity of the FTIR spectra bands were observed despite the low content of extract added to the films. Due to this fact, the antioxidants were extracted and identified by spectroscopic analysis; and they were also quantified using the Folin-Denis method and a gallic acid calibration curve, which confirmed the presence of natural antioxidants in the films. According to the SEM analysis, the presence of natural antioxidants has no influence on the film morphology because the stretch marks and white points that were observed were related to starch presence. On the other hand, the TGA analysis showed that the type of extract influences the total weight loss. The overall interpretation of the results suggests that the use of natural antioxidants as additives for chitosan-starch film preparation has a prominent impact on most of the critical properties that are decisive in making them suitable for food-packing applications.

Covalently Bonded Chitosan on Graphene Oxide via Redox Reaction.

Carbon nanostructures have played an important role in creating a new field of materials based on carbon. Chemical modification of carbon nanostructures through grafting has been a successful step to improve dispersion and compatibility in solvents, with biomolecules and polymers to form nanocomposites. In this sense carbohydrates such as chitosan are extremely valuable because their functional groups play an important role in diversifying the applications of carbon nanomaterials. This paper reports the covalent attachment of chitosan onto graphene oxide, taking advantage of this carbohydrate at the nanometric level. Grafting is an innovative route to modify properties of graphene, a two-dimensional nanometric arrangement, which is one of the most novel and promising nanostructures. Chitosan grafting was achieved by redox reaction using different temperature conditions that impact on the morphology and features of graphene oxide sheets. Transmission Electron Microscopy, Fourier Transform Infrared, Raman and Energy Dispersive spectroscopies were used to study the surface of chitosan-grafted-graphene oxide. Results show a successful modification indicated by the functional groups found in the grafted material. Dispersions of chitosan-grafted-graphene oxide samples in water and hexane revealed different behavior due to the chemical groups attached to the graphene oxide sheet.